1. Field of the Invention
This invention relates generally to the field of 3-D printing and 3-D stereo imaging technologies. More particularly, it relates to the field of computer hard copy output devices that produce 3-D images. Still more particularly, it relates to the production of 3-D movies, slide projection images, 3-D portraits, paintings and the like and the resulting products.
2. Description of Related Art
Because of their large birefringence and electro-optical properties, liquid crystals are materials which are becoming pervasive in our daily lives. They are found in wristwatches, calculators, and computer displays. Liquid crystals are found in three general broad classes: Smectic, Nematic; and Cholesteric (see Jacobs et al, U.S. Pat. No. 5,054,888); Jacobs et. al., Journal of the Optical Society of America, B, Vol. 5 (9), pp 1962-1978 (September 1988); Martin Schadt and Jurg Funfschilling, Society of Information Displays, SID 90 DIGEST, p 324 (1990); and Robert Maurer, et. al., Society of Information Displays, SID 90 DIGEST, p 110 (1990). Cholesteric Liquid Crystals (CLC) form left handed or right handed helical structures with a helix pitch, P. The structure of an aligned cholesteric liquid crystal consists of multi-layers (parallel planes). Each layer has rod-like molecules which are ordered in a specific orientation in the direction of a director. The orientations of the directors of successive layers (planes) describe a helical path which is either left-handed (LH), or right-handed (RH). These materials are optically active and have an optical axis parallel to the helix axis and perpendicular to the molecular planes. An (RH) film prepared with its optical axis perpendicular to the film exhibits the property of selective reflection when a monochromatic beam of wavelength, .lambda., propagating along the helix axis satisfies the relationship EQU .lambda.=.lambda..omicron.=n.sub.a P (1)
where n.sub.a is the average refractive index of the CLC material and P as its pitch. Unpolarized light with wavelength .lambda.=.lambda..omicron. incident on the film interacts with the helix structure and reflects 50% of its intensity as right circularity polarized light (RCP), and the other 50% is transmitted as left circularly polarized light (LCP) through the film. If one incident light has one or more wavelengths that are not equal to .lambda..omicron., all the light is transmitted. Note that equation (1) is strictly valid in the case where the angle of incidence .theta. (measured from the helix axis) is zero For a non-zero value of .theta., the effective value of .lambda..omicron. shifts to a shorter wavelength, .lambda..theta., given by EQU .lambda..theta.=.lambda..omicron.[cos{sin.sup.-1 (sin.theta./n.sub.a)}](2)
In all subsequent discussions in this application, whenever .theta..noteq.0, it is implied that .lambda..omicron. means .lambda..theta. as given by Eq. 2. If the film has an LH helix, and the incident unpolarized light satisfies .lambda.=.lambda..omicron., 50% of the selectively reflected polarized light will have the LCP state, and the other 50% transmitted through the film will have the RCP state. The selective reflection wavelengths according to Eq. 1 are obtained by the pitch length which is a material property that may be varied by varying the chiral concentration or the concentration of the mesogenic side-groups (see U.S. Pat. No. 4,410,570). Thus, the CLC materials may be prepared to produce the three additive primary colors; red, green, and blue or any other color. It is important to note that this selective reflection polarizing property does not involve or depend on an absorptive mechanism as in the case of conventional color pigments, dyes and sheet polarizers.
A fundamental property of light is that it can have only two independent, mutually orthogonal polarization states, either circular LCP and RCP states or linear states. Embodiments shown in the present application utilize the well-known phenomenon that LCP light incident on a metallic reflector is converted into RCP light because the metal causes a phase shift of 180.degree. between the independent electric field vector components. Similarly, a quarter-water retarder causes a 90.degree. phase shift and converts a circularly polarized light into linear polarized light or a linear polarized light into circularly polarize light. Also, a half-wave retarder converts RCP light into LCP light and vice versa by causing a phase shift between the independent electric field vector components.
The present invention relies On CLC materials in the solid state at the operation temperature. Such CLC polymers have been synthesized in the LH and RH formulations (See Tsai et al, Appl. Phys. Lett., 54, 2395 (1989)).